Some auto-focus apparatuses (focusing apparatuses) used in digital cameras, digital video cameras, and the like create a signal for evaluating a focused state using a video signal obtained from an image sensing element and determine a focus position using the signal. Since such a method does not require a sensor exclusively used for auto-focus, the method has an advantage that cost is low, parallax is not present, and accuracy is high. However, it is necessary to drive a focus lens within a predetermined distance range to sequentially create evaluation signals. Thus, when the focus lens needs to be driven over a relatively wide range because the focal length of the lens is long or a full aperture F value is small, for example, there is a disadvantage that it takes considerably a long time to attain an in-focused state.
As a method coping with this problem, for example, a method described in Japanese Patent No. 2708904 is known. In an invention of the patent, a subject distance range is searched through in a relatively coarse step to specify a relative maximum of an evaluation value and the distance range near this relative maximum is searched again in a fine step to determine a focus position. According to this method, when a search range is sufficiently large, since the total number of data to be acquired decreases compared with the case in which the subject distance range is searched throughout only in the fine step, it is possible to reduce a time to attain an in-focus state.
However, in the method described above, since after searching the subject distance range in the coarse step, search in the fine step is always performed, it is necessary to cause the focus lens to operate reciprocatingly many times. Thus, it sometimes takes a long time to attain in-focus state (focusing time).